In the CDMA 1xRTT system, the forward radio resources, which include Walsh Code (WC) and Power, are shared by Voice channels and Data channels. Further more, there are two sub-types of data channels, namely Fundamental Channels (FCH) and Supplemental Channels (SCH).
Data calls or sessions can be divided into those which have a real-time packet transmission requirement, and those which do not. For example, a voice call requires real-time transmission in order to maintain the interactive nature of a conversation, whereas a file download or email message does not. Call types with a real-time requirement include Push-to-Talk (PTT) sessions and Voice over IP (VoIP) telephone calls. Note that real-time actually implies near real-time; and should be understood to require transmission without noticeable delay. Due to the nature of conversations, and the way speech is packetized, the packets do not actually need to be transmitted instantaneously as long as the speech is received at the far end without any noticeable delay.
Many data sessions without a real-time requirement desire higher bandwidth than is required for a typical VoIP call, but can withstand noticeable delays between the transmission of packets, and still be successfully received. Typically such transmissions are called bursty in nature, as they typically receive a series of packets in bursts, with gaps or delays between each burst. A file transfer is one example. There is no real-time requirement, as the receiving application can simply wait out any delays in transmission, but the bandwidth requirement is higher than a typical voice call, as there is more data that needs transmission than is required by a VoIP call. Every data call or session requires a data FCH, and those data calls or sessions which do not have a real time requirement, but which require higher bandwidth than can be provided by an FCH call, require one or more SCH bursts as required. The former defines the number of data users in a sector while the later provides additional data throughput per user.
One problem with this division of channels is that the demand for resources for data calls is inherently variable. Some services will require large data transfers. This can take a substantial amount of resources over a short period of time, or it can take a smaller amount of resources spread over a longer duration. It is desirable to allow variable transfer rates, in order to maximize resource utilization. If there is heavy demand for resources during some periods of time, and less in others, it is desirable to provide significant bandwidth to a file transfer during non-busy periods, in order to free up resources during busier periods. This will obviously reduce waiting time for users who perform data transfers during less busy periods. In order to ensure sufficient bandwidth for data transfers, conventional network design reserves a minimum amount of resources for the SCH.
However, a problem with permitting variable transfer rates is that data transfers, once commenced, can utilize a significant share of resources. This can lead to insufficient resources available to new requests for services once such a transfer commences, leading to blocked calls.
In order to provide minimum service levels, resources are typically partitioned by a base station resource manager in order to ensure a minimum level of service is available to all 3 types of channels (namely the voice FCH channels (VCs), the data FCHs and data SCHs).
This typically implies that there is an upper limit to the amount of resources (i.e., WC and power) used by each of the VC's, FCHs and SCHs. In other words the resources are partitioned between the VC's, FCHs and SCHs. While this tends to satisfy the requirement of ensuring minimum service levels for each set of channels, and also tends to allow data transfers while still allowing a specified minimum number of data calls, this often does not lead to the maximal use of resources. Furthermore, if the resources for each Channel type are fully utilized, any new request for service that requires such a channel will be blocked. This can happen even if there are substantial unused resources being reserved by the other channel types.
It is difficult to solve this problem without favoring one service (i.e., channel type) over another. For example, one approach, as will be discussed below with reference to FIG. 1, favors SCH throughput at the expense of number of data users (FCH).
Thus, there is a need for a better system of managing resources to avoid unnecessary call blocking, while providing for minimum levels of service.